SILVER SPRING, Md. (AP) - A previously rejected weight loss pill won an overwhelming endorsement from public health advisers Wednesday, raising hopes that the drug from Vivus Inc. could become the first new anti-obesity medication to reach the U.S. market in more than a decade.

The Food and Drug Administration has rejected three weight loss pills in the last two years, including Vivus’ pill Qnexa, due to safety concerns. Experts agree new weight loss drugs are needed to treat an estimated 75 million obese adults in the U.S., but the string of rejections has raised questions of whether any pharmaceutical treatment is safe enough to win approval.

At a public meeting Wednesday, an FDA panel of outside physicians voted 20-2 in favor of the weight loss drug from Vivus, setting the stage for a potential comeback for a drug that has been plagued by safety questions since it was first submitted to the agency in 2010.

Nearly all the panelists backed the drug due to its impressive weight loss results, with most patients losing nearly 10 percent of their overall weight after a year on the drug. But the group stressed that the drugmaker must be required to conduct a large, follow-up study of the pill’s effects on the heart. Studies of Qnexa show it raises heart rate and causes heart palpitations, a longtime concern with diet pills over the years. The group of experts said it is still unclear if those side effects lead to heart attack and more serious cardiovascular problems.

“The potential benefits of this medication seem to trump the side effects, but in truth, only time will tell,” said Dr. Kenneth Burman of the Washington Hospital Center.

The FDA is not required to follow the advice of its panels, though it often does. A final decision on the drug is expected by mid-April.

In a key question, the physicians said Vivus could conduct the cardiovascular safety study after FDA approval. A requirement to conduct the study ahead of market approval would cost the company millions of dollars and take at least three more years.

“There is an urgent need for better pharmacologic options for individual patients with obesity,” said Dr. Elaine Morrato, of the University of Colorado. “I believe Qnexa demonstrated a meaningful efficacy benefit and that there are consequences to not treating obesity.”

Vivus, based in Mountain View, Calif., is one of three small drugmakers racing to bring the first new prescription weight loss drug to market in more than a decade. In the past two years the Food and Drug Administration has rejected pills from all three: Arena Pharmaceuticals Inc., Orexigen Therapeutics Inc. and Vivus. All three companies are in the process of resubmitting their products.

The FDA rejected Qnexa in October 2010, citing numerous side effects including elevated heart rate, psychiatric problems and birth defects. Vivus has resubmitted the drug with additional follow-up information on safety, hoping for a more favorable ruling.

“Right now there aren’t any good treatments out there besides dieting and bariatric surgery — clearly there’s a huge gap,” Tam said.

With U.S. obesity rates nearing 35 percent among adults, doctors and public health officials say new weight-loss therapies are desperately needed. And even a modestly effective drug could have blockbuster potential. Analysts expect a new weight loss pill to garner at least 10 million users within a few years.

Qnexa is a combination of two older drugs: the amphetamine phentermine, which is approved for short-term weight loss, and topiramate, an anti-seizure and anti-migraine drug sold by Johnson & Johnson as Topamax. Phentermine helps suppress appetite, while topiramate is supposed to make patients feel more satiated.

Along with heart safety, panelists raised concerns about potential birth defects in women who become pregnant while taking Qnexa: topiramate is known to more than double the risk of birth defects.

There were 34 pregnancies among 3,386 women enrolled in Vivus’ studies of Qnexa, despite precautions to make sure women used contraception. An FDA expert on birth defects estimated there would be five babies born with a cleft lip defect for every 1,000 women who became pregnant while taking Qnexa.

If approved, FDA scientists said they would require Vivus to train prescribers to educate patients on the pregnancy risks of Qnexa. The drug would only be available from 10 mail-order pharmacies.

Qnexa’s other ingredient, phentermine, was one half of the dangerous fen-phen combination, a weight loss treatment pushed by doctors that was never approved by the FDA. The regimen was linked to heart-valve damage and lung problems in the late 1990s, and the FDA forced drugmaker Wyeth to withdraw two versions of its drug fenfluramine.

Fen-phen is just one example in the decadeslong history of failed weight loss drugs, which have continued to pile up in recent years.

Four years ago Sanofi-Aventis SA discontinued studies of its highly anticipated pill Acomplia due to psychiatric side effects, including depression and suicidal thoughts. In 2010, Abbott Laboratories withdrew its drug Meridia after a study showed it increased heart attack and stroke. The drug won approval in 1997 in the wake of the recall of fenfluramine but never achieved widespread use due to modest weight loss and safety concerns. Only 100,000 prescriptions were written in the U.S. during Meridia’s last full-year on the market.

Currently there is just one prescription drug on the market for long-term weight loss: Roche’s Xenical, which is sold over the counter as alli by GlaxoSmithKline. The drug is not widely used because of modest weight loss results and unpleasant side effects, including gas and diarrhea.